The invention resides in a process of producing an encapsulated detector which is operating in an ultra high vacuum (UHV) and which is suitable for use as a gamma (.gamma.) spectrometer, particularly with an encapsulated germanium (Ge) detector. The detector includes a chamber defined by a containment pot, which is closed by means of a containment lid after the detector is mounted in the detector chamber. The present invention also relates to a capsule for a detector operating at UHV.
For the spectroscopy of .gamma.-radiation in many areas of research and the industry, detectors of highly purified germanium (HPGe) are utilized. These detectors have a very good energy resolution and a high detection efficiency, properties which facilitate an application in basic nuclear-physical research and in space research but also in environmental monitoring, radiation protection, non-destructive material analysis and industrial manufacturing monitoring.
In order to become operative, Ge-detectors need to be cooled down to about -190.degree. C. by liquid nitrogen. For this purpose the detectors are installed in a vacuum cryostat which, at the same time, protects the very sensitive surfaces of the detectors. The present cryostat technology makes handling and servicing of the detectors difficult and makes it hard to use the same detector for different measuring tasks.
Encapsulated detectors are used for example as .gamma.-spectrometers for studying fast moving atomic nuclei produced in heavy ion reactions. In order to limit the broadening of the .gamma.-lines caused by the inherent Doppler effects, it is desirable to minimize the solid angle of the detectors and the detectors should have a high granularity. In the interaction between .gamma.-radiation and detector materials, scattering occurs in addition to the desired photo effect to be detected, particularly the so-called Compton scattering, which provides for a continuous background in the .gamma.-radiation spectrum and which deteriorates the detector response function. To minimize this Compton scattering background, the detector is made as large in volume as possible. In addition, an anti-Compton detector is utilized by which the scattered radiation escaping from the detector can be detected and suppressed.
By mounting the detectors in evacuated capsules, a high reliability can be achieved for the experimental results obtainable with the detectors. The highly sensitive surfaces of the detector crystals are protected in the ultra highly evacuated chamber. In this way, handling of the detectors becomes quite simple, particularly during regeneration after radiation damage. Encapsulated detectors can also be advantageously arranged in clusters comprising several detectors so that, by adding the energies deposited in the various detectors in the case of Compton scattering, the total energy of a .gamma.-quantum can be determined with high accuracy.
In order to obtain a compact structure, particularly for a cluster arrangement, the capsules have to surround the detector crystals as closely as possible. During the vacuum sealing of the capsules after mounting of the detectors, care is to be taken that the quality of the detectors remains undisturbed during closing of the capsules and that they are enclosed in such a manner that the detector chamber remains ultra high vacuum tight for long periods of operation.
It is the object of the present invention to provide a method of producing a capsule for a detector operating in a UHV, wherein the quality of the detector is not detrimentally affected by a capsule surrounding the detector as closely as possible.